JP3537560B2 - Current-voltage converter and optical receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current-to-voltage converter and an optical receiver, and more particularly to a transimpedance circuit for converting a received light signal into a voltage in a device using light as a communication medium. .

[0002]

2. Description of the Related Art In recent years, many devices using light as a communication medium have been developed, and these devices use an optical receiver that receives light and outputs a voltage. In order to convert a received light signal into a voltage in the optical receiver, a current-voltage conversion circuit is required. An apparatus using an optical receiver is driven by a commercial power supply,
There are many types that are driven by battery power.
Therefore, it can be driven with a wide range of power supply voltage, and
A circuit that can output a voltage with a wide dynamic range is desired.

FIG. 8 is a configuration diagram of an optical receiver according to a conventional example. In FIG. 8, reference numeral 1 denotes a light receiving element that receives light such as infrared light and generates a photocurrent. As the light receiving element 1, a photodiode (PD) is used. Reference numeral 2 denotes a current-voltage conversion circuit that converts a photocurrent of the light receiving element 1 into a voltage. The conversion circuit 2 includes two npn-type bipolar transistors Q
1, Q2, one diode D1, and three resistors R1
To R3.

The collector of the transistor Q1 is connected to one end of the resistor R1 and the base of the transistor Q2. The base (input) of the transistor Q1 is connected to the light receiving element 1, the cathode of the diode D1, and one end of the resistor R3, respectively. Is connected to the ground line GND. Transistor Q2
Is connected to the power supply line VCC, and its emitter is connected to the output, one end of the resistor R2, the other end of the resistor R3, and the anode of the diode D1. Resistance R1
Is connected to the power supply line VCC, and the other end of the resistor R2 is connected to the ground line GND. R3 is called transimpedance.

The diode D1 clamps a voltage drop of the resistor R3. D1 turns on when the photocurrent Ipd flowing through the light receiving element 1 increases. At this time, the on condition of D1 is that the voltage drop of the resistor R3 is
1 when the forward voltage drop VF is exceeded. When the diode D1 is turned on, a current flows from the transistor Q2 to the light receiving element 1, and the base potential of the transistor Q1 is fixed to prevent the collector potential from rising.

3 is an output voltage V of the current-voltage conversion circuit 2
2 is a DC voltage feedback circuit for feeding back 2 to the input. The feedback circuit 3 includes a differential amplifier, and outputs the output voltage V2 and the reference voltage Vre.
The input potential of the transistor Q1 is controlled so that f and f have the same potential. Next, the operation of the optical receiver will be described. For example, when light, which alternates between light and dark, is received by the light receiving element 1, a photocurrent Ipd flows through the light receiving element 1. The photocurrent Ipd constitutes an “H” (high) level and an “L” (low) level logic according to light brightness and darkness.

For example, when the photocurrent Ipd does not flow, the current-voltage converter 2 includes transistors Q1, Q2, and a resistor R2.
Since a negative feedback circuit is formed by R1 and R2, the DC potentials of the input V1 and the output V2 are the same (V1 = V2 = Vbe). On the other hand, when the photocurrent Ipd flows, ΔV2 = ΔIdd · R as the voltage change amount of the output V2 of the current-voltage converter 2.
3 is obtained. Thus, current-voltage conversion using R3 as a transimpedance can be performed. Note that when the photocurrent Ipd flowing through the light receiving element 1 increases and the voltage drop of the resistor R3 exceeds the forward voltage VF of the diode D1, the diode D1 turns on and current flows from the transistor Q2 into the light receiving element 1. As a result, the transistor Q1 is clamped.

The DC feedback amplifier 3 eliminates (cancels) a leak current of the light receiving element 1 and an offset current due to extraneous light superimposed on the optical signal.

[0009]

However, the conventional current-voltage conversion circuit 2 has the following problem because the diode D1 for clamping the transistor Q1 is connected to both ends of the resistor R3. When the photocurrent Ipd shifts from the “H” level to the “L” level, the output waveform becomes like a tail as shown in the dashed circle in FIG. This is because the influence of the parasitic capacitance inside the light receiving element 1 and the electric charge accumulated in the diode D1 are discharged. This charge accumulates in the diode D1 after the current has passed through the light receiving element 1. When the input current is large, the output waveform further trails, so that the dynamic range of the current-voltage conversion circuit is narrowed. Then, there is a possibility that an analog / digital conversion circuit or the like connected at a subsequent stage may malfunction. Further, if it takes time for the electric charge accumulated in the diode D1 to escape, the frequency response characteristics of the optical receiver deteriorate.

Incidentally, the diode D1 is connected to the transistor Q1.
Needed to clamp. This is the light receiving element 1
When large light is irradiated on the light receiving element 1, a large current flows through the light receiving element 1,
The base potential of transistor Q1 drops to the potential of ground line GND. As a result, Q1 deviates from the operating point. For this reason, Q1 is clamped. The current flowing through the transistor Q1 is determined by the power supply voltage and the load resistance R1 of Q1. Therefore, the current flowing through Q1 flows in proportion to the power supply voltage. As a result, when the current flowing through Q1 changes due to an extremely low power supply voltage or a large increase on the contrary, the frequency response characteristic of Q1 also changes. Q
The frequency response characteristic of 1 greatly changes the frequency output characteristic of the optical receiver. For this reason, if the current flowing through Q1 changes significantly due to the power supply voltage, the frequency output characteristics of the optical receiver will change significantly.

Further, considering the operation limit of the current-voltage conversion circuit at the time of low voltage driving, when the power supply voltage VCC becomes equal to or lower than the voltage drop of the resistor R1 + 2 × Vbe + VF, the circuit does not operate. For this reason, it has hindered low-voltage driving of the optical receiver. Vbe is a voltage between the base and the emitter of Q1 or Q2. VF is diode D1
Is the forward voltage drop. Since the diode and the transistor in the same chip are formed by the same junction, VF ≒ Vbe.

The present invention has been made in view of the problems of the conventional example, and a current-voltage converter capable of converting a current into a voltage with a wide range of power supply voltage while maintaining a clamping function. The purpose is to provide a receiver and an optical receiver.

[0013]

As shown in FIG. 1, a first current-to-voltage converter according to the present invention has a first transistor having a base connected to an input, and one end connected to the first transistor. A first resistor connected to the collector of the first transistor, a second resistor having one end connected to the other end of the first resistor, and the other end connected to a first power supply line, and a base connected to the first resistor; A second transistor connected to a connection point between the first resistor and the second resistor and having a collector connected to the first power supply line;
A first constant current source having one end connected to the emitter and the output of the second transistor, and the other end connected to a first power supply line, one end connected to the emitter of the second transistor, and A third resistor having the other end connected to the base of the first transistor, and a second resistor having one end connected to the emitter of the first transistor and the other end connected to the second power supply line. A current source, a capacitance having one end connected to the emitter of the first transistor, and the other end connected to the second power supply line, a base connected to the collector of the first transistor, and an emitter connected A third transistor connected to a base of the first transistor and having a collector connected to a first power supply line.

In the first current-to-voltage converter according to the present invention, a feedback circuit is provided for detecting a voltage across the third resistor and adjusting a base potential of the first transistor. I do. In the first current-voltage converter of the present invention, a low-pass filter is provided in the feedback circuit.

In the first current-voltage converter of the present invention, the value of the second resistor is set so that the third transistor is cut off when there is no input to the first transistor. It is characterized by. As shown in FIG. 4, the second current-to-voltage converter of the present invention has a gate connected to the collector of the first transistor instead of the third transistor, and a source connected to the third transistor. A field effect transistor connected to the base of the first transistor and having the drain connected to the first power supply line;
The field effect transistor is characterized in that the threshold voltage is adjusted to a value larger than the voltage drop between the base and the emitter when the second transistor is turned on.

A third current-to-voltage converter according to the present invention, as shown in FIG. 5, has a cathode connected to the collector of the first transistor in the first current-to-voltage converter. And a Schottky barrier diode having an anode connected to the base of the first transistor. As shown in FIG. 6, the fourth current-to-voltage converter of the present invention has a first
In the current-voltage converter, a diode having a cathode connected to the collector of the first transistor and an anode connected to the first power supply line is provided.

As shown in FIG. 7, a fifth current-to-voltage converter according to the present invention has a first field effect transistor having a gate connected to an input, and one end connected to the first field effect transistor. A first resistor connected to the drain of the transistor, a second resistor having one end connected to the other end of the first resistor, and the other end connected to the first power supply line, and a gate connected to the first resistor. A second field effect transistor having a drain connected to a first power supply line, and one end connected to a source and an output of the second field effect transistor. And a first constant current source having the other end connected to the first power supply line, one end connected to the source of the second field effect transistor, and the other end connected to the first field effect transistor. A third resistor connected to the gate;
A second constant current source having one end connected to the source of the first field effect transistor and the other end connected to a second power supply line; and one end connected to the source of the first field effect transistor. And a capacitor having the other end connected to the second power supply line, a gate connected to the drain of the first field-effect transistor, a source connected to the gate of the first field-effect transistor, and And a third field-effect transistor having a drain connected to the first power supply line.

According to a sixth current-voltage converter of the present invention, the threshold voltage of the third field-effect transistor is adjusted to a value larger than the threshold voltage of the second field-effect transistor. And The optical receiver of the present invention includes a light receiving element that converts received light into a current, and a current-voltage conversion circuit that converts a current flowing through the photoelectric element into a voltage, wherein the current-voltage conversion circuit is a first to a first. A sixth aspect of the present invention is characterized by comprising a current-voltage converter, and achieves the above object.

The operation of the first current-to-voltage converter of the present invention will be described. For example, when the input current does not flow through the first transistor, the DC potential of the input and the output of the current-voltage converter are the same. The DC potential of the input and output is a potential obtained by substantially subtracting the voltage drop of the resistor R2 and the voltage drop between the base and the emitter of the second transistor from the power supply voltage.
The emitter potential of the first transistor is a DC voltage obtained by subtracting the base-emitter voltage drop of the first transistor from the input voltage of the current-to-voltage converter. Further, since the emitter of the first transistor is grounded in an AC circuit by a capacitor, this transistor circuit is a so-called grounded emitter circuit.

Since the input voltage and the output voltage of the current-to-voltage converter are at the same potential, the feedback circuit does not feed back the control signal to the input of the first transistor. On the other hand, since the third transistor for clamping also goes through the same process as the second transistor, the voltage drop between the base and the emitter is the same. Therefore, the base voltage of the third transistor is smaller than the base voltage of the second transistor by the voltage drop of the first resistor.
No collector current flows through the transistor. As a result, the third transistor does not perform the clamp operation.

Next, when an input current flows through the first transistor, the output of the current-voltage converter is ΔV2 = ΔI
pd × R3. Here, ΔV2 is a change in the output of the current-voltage converter, and ΔIpd is a change in the input current of the first transistor. R3 is a third resistor. Thus, the current-voltage conversion circuit using R3 as the transimpedance operates.

On the other hand, when the amplitude of the input current flowing through the first transistor is large, the collector current of the first transistor decreases, and the collector potential increases. Thus, the third transistor draws current from the power supply potential and clamps the first transistor. At this time, the output of the current-voltage converter is ΔV2 = ΔIpd described above.
× R3 no longer holds, and the output is V2 = VC
C-R2 · I1-Vbe. Here, V2 is a DC output of the current-voltage converter, VCC is a power supply voltage, and R
2 is a second resistor, I1 is a current flowing through the first transistor, and Vbe is a base current of the second transistor.
This is the voltage drop between the emitters.

When the input current flowing through the first transistor changes from “H” level to “L” level, the electric charge accumulated at the base of the third transistor becomes
It is pulled out by the first transistor. Thus, according to the first current-voltage converter of the present invention, when the base input of the first transistor falls from the “H” level to the “L” level, the base input of the third transistor is connected to the base / emitter of the third transistor. Since the accumulated charge is extracted by the first transistor, the output waveform can be sharply lowered as compared with the case where a clamp diode as in the related art is used.

Accordingly, the dynamic range of the current-to-voltage conversion circuit can be widened by causing the output waveform to fall sharply as compared with the conventional example. According to the first current-to-voltage converter of the present invention, the current flowing through the first transistor is determined by the first constant current source. The collector current can be kept constant. As a result, the frequency response characteristics of the first transistor are stabilized.

Further, according to the first current-to-voltage converter of the present invention, considering the operation limit at the time of driving the circuit at a low voltage, the power supply voltage VCC becomes the resistance drop (R1 + R2) + 2 ×
The circuit can be operated until Vbe or less. Vbe is a voltage drop between the base and the emitter of the first transistor and the second transistor. Further, in the first current-to-voltage converter of the present invention, since the feedback circuit that detects the voltage across the third resistor adjusts the base potential of the first transistor, a DC offset is superimposed on the input signal. This can be excluded. Further, by providing a low-pass filter in the feedback circuit, a high-frequency cutoff frequency of the current-voltage converter can be determined. The low-pass filter passes a signal having a frequency lower than this frequency.

According to the second current-to-voltage converter of the present invention, the field effect transistor provided in place of the third transistor has a value larger than the voltage drop between the base and the emitter when the second transistor is turned on. , The field effect transistor can be turned on when the input current increases. As a result, the resistance R1 that determines the operation of the field effect transistor
Can be omitted. Therefore, it contributes to circuit integration.

According to the third current-to-voltage converter of the present invention, since the Schottky barrier diode is connected between the base and the collector of the first transistor, the Schottky barrier diode is connected with reference to the base potential of the first transistor. This prevents the collector voltage from dropping. Therefore, even when the input current is large, the circuit operation is stabilized because the collector voltage of the first transistor does not decrease.

According to the third current-to-voltage converter of the present invention, the diode is connected between the collector of the first transistor and the first transistor.
, The collector voltage of the first transistor can be prevented from lowering with reference to the first power supply line. Therefore, even when the input current is large, the circuit operation is stabilized because the collector voltage of the first transistor does not decrease similarly to the second current-to-voltage converter.

According to the fifth current-to-voltage converter of the present invention, in the first to fourth current-to-voltage converters, the signal input circuit and the signal output circuit are constituted by the field effect transistors. Can be integrated. According to the sixth current-to-voltage converter of the present invention, since the threshold voltage of the third field-effect transistor is adjusted to a value larger than the threshold voltage of the second field-effect transistor, the input current becomes large. When this happens, the third field-effect transistor can be turned on. Thus, the resistor R1 that determines the operation of the third field-effect transistor can be omitted. Therefore, it contributes to circuit integration.

According to the optical receiver of the present invention, since the current-to-voltage converter is composed of any one of the first to sixth current-to-voltage converters, it can be driven with a wide range of power supply voltage. Moreover, the dynamic range of the current-voltage converter can be expanded. In addition, the first of the current-voltage conversion circuit
Since the frequency response characteristics of the transistor do not depend on the power supply voltage, the frequency output characteristics of the optical receiver are also stable. Further, when the power supply voltage VCC is reduced by the resistance drop (R1 + R
2) Since the current-voltage conversion circuit can be operated until the voltage becomes equal to or less than + 2 × Vbe, low voltage driving of the optical receiver can be achieved.

[0031]

Next, an embodiment of the present invention will be described with reference to the drawings. 1 to 7 are explanatory diagrams of a current-voltage converter and an optical receiver according to an embodiment of the present invention. (1) First Embodiment FIG. 1 is a configuration diagram of an optical receiver using a current-voltage converter according to a first embodiment of the present invention, and FIG.
FIG. 2 shows a configuration diagram of a C feedback circuit. In FIG. 1, reference numeral 11 denotes a light receiving element (photodiode: PD) that receives light such as infrared light and generates a photocurrent. The light receiving element 11 utilizes a photoelectric effect of converting light into a current.

Reference numeral 12 denotes a current-voltage conversion circuit for converting a current flowing through the light receiving element 11 into a voltage. The current-to-voltage converter 12 includes the first current-to-voltage converter of the present invention. In FIG. 1, the conversion circuit 12 includes three npn-type bipolar transistors (hereinafter simply referred to as transistors) Q1 to Q3, three resistors R1 to R3, two constant current sources I1 and I2, and one capacitance. C1.

The transistor Q1 is an example of a first transistor, and its base (input) is connected to the light receiving element 11, the emitter of the transistor Q3, and one end of the resistor R3, and its collector is connected to the base of the transistor Q3 and the resistor R1. Connect to one end respectively. The emitter of the transistor Q1 is connected to the constant current source I1 and one end of the capacitance C1. The constant current source I1 is an example of a first constant current source. The other end of the capacitance C1 is connected to the ground line GND. The capacitance C1 determines the low cut frequency of the transistor Q1.

The other end of the resistor R1 is connected to the base of the transistor Q2 and one end of the resistor R2. The other end of the resistor R2 is connected to the power supply line VCC. It is desirable that the value of the resistor R2 be set so that the transistor Q3 is cut off when there is no input to the transistor Q1. The transistor Q2 is an example of a second transistor, and its collector is connected to the power supply line VCC, and its emitter is connected to the output, the other end of the resistor R3, and the constant current source I2. The constant current source I2 is an example of a second constant current source, and the other end is connected to the ground line GND. The resistance R3 is called transimpedance.

The transistor Q3 is an example of a third transistor, and forms a clamp transistor. Its collector is connected to the power line VCC. Transistor Q3
Is for clamping the transistor Q1. The transistor Q3 turns on when the photocurrent Ipd flowing through the light receiving element 11 increases. The ON condition of Q3 at this time is when the photocurrent Ipd increases, the collector current of Q1 decreases, and the collector voltage increases. When the transistor Q3 is turned on, the power supply line VCC connects the light receiving element 1
1 to fix the base potential of the transistor Q1 to prevent the collector potential from dropping.

Reference numeral 13 denotes a DC feedback circuit which detects the voltage between both ends of the resistor R3 and adjusts the base potential of the transistor Q1, and is an example of a feedback circuit. 2A, the DC feedback circuit 13 includes a differential amplifier and an output circuit. The differential amplifier comprises three pnp type bipolar transistors Q13 to Q15, two npn type bipolar transistors Q11 and Q12, and two constant current sources I
12, I12 and capacitance C11.

In FIG. 2A, the base of transistor Q11 is connected to the-terminal, and the base of transistor Q12 is connected to the + terminal. The emitters of the transistors Q11 and Q12 are connected to a constant current source I11. The collector of transistor Q11 is connected to the collector of transistor Q13. The collector of transistor Q12 is connected to the collector of transistor Q14. The base of transistor Q13 is transistor Q14.
And the collector of the transistor Q11. The emitters of the transistors Q13 and Q14 are connected to the power line V.
Connect to CC. The collector of the transistor Q14 is connected to the base of the transistor Q15 and one end of the capacitance C11.
The other end of the capacitance C11 is connected to the ground line GND. The emitter of transistor Q15 is connected to power supply line VCC. Its collector is connected to the output and to a constant current source I12.

The DC feedback circuit 13 can make the output DC potential constant by adjusting the base potential of the transistor Q1 to be constant. In FIG. 2B, reference numeral 13A denotes a feedback circuit obtained by modifying the DC feedback circuit 13, and is provided with a filter resistor R11. The resistance R11 forms a low-pass filter together with the capacitance C11. The low-pass filter determines a high cut frequency of the DC feedback circuit 13.

FIG. 3A is a diagram for comparing output waveforms of an optical receiver using the current-voltage converter according to each embodiment of the present invention and a conventional optical receiver. . FIG.
(B) shows the frequency characteristics of the optical receiver according to each embodiment of the present invention. The vertical axis is gain, and the horizontal axis is frequency. fL is a low frequency cut frequency. The optical receiver is f
It allows signals with frequencies higher than L to pass.

Next, the operation of the optical receiver using the current-to-voltage converter according to the first embodiment of the present invention will be described with reference to FIG. For example, when light (predetermined frequency) in which light and dark are alternately repeated is received by the light receiving element 11, a photocurrent Ipd flows through the light receiving element 11. The photocurrent Ipd constitutes an “H” (high) level and an “L” (low) level logic according to the brightness and darkness of light as shown in FIG.

For example, when the photocurrent Ipd does not flow through the transistor Q1, the DC potential of the input V1 and the DC potential of the output V2 of the current-voltage conversion circuit 12 are the same. Input V1 and output V
2 is obtained by subtracting the voltage drop R2 · I1 of the resistor R2 and the voltage drop Vbe between the base and the emitter of the transistor Q2 from the power supply voltage VCC (ΔVCC−R2
I1-Vbe).

The emitter potential of the transistor Q1 is different from the input voltage V1 of the current-voltage conversion circuit 12 by the transistor Q1.
1 is a DC voltage (V1-Vbe) obtained by subtracting the voltage drop between the base and the emitter. Further, since the emitter of the transistor Q1 is grounded in the form of an AC circuit by the capacitor C1, this transistor circuit is a so-called grounded emitter circuit.

The DC feedback circuit 13 does not feed back the control signal to the input V1 of the transistor Q1 because the input V1 and the output V2 of the current-voltage conversion circuit 12 have the same potential. On the other hand, the base of the transistor Q3 for clamping
The voltage drop Vbe between the emitters is different from that of the other transistors Q1,
Since the voltage drop between the base and the emitter of Q2 is larger than Vbe, no collector current flows through transistor Q3.

Next, when the photocurrent Ipd flows through the transistor Q1, the output V2 of the current-voltage conversion circuit 12 becomes ΔV
V2 = ΔIdd × R3. Here, ΔV2 is a change in the output of the current-voltage conversion circuit 12, and ΔIpd is a change in the photocurrent Ipd flowing through the transistor Q1. R3 is the value of the resistor R3. Thus, the current-voltage conversion circuit using R3 as the transimpedance operates.

On the other hand, the photocurrent I flowing through the transistor Q1
When the amplitude of pd is large, the collector current of the transistor Q1 decreases, and the collector potential increases. As a result, the transistor Q3 draws current from the power supply potential and clamps the transistor Q1. The output V2 of the current-voltage conversion circuit 12 at this time is ΔV2 described above.
= ΔIdd × R3 does not hold, and the output V2
Is V2 = VCC-R2.I1-Vbe.

Here, V2 is D of the current-voltage conversion circuit 12.
C is a power supply voltage, VCC is a power supply voltage, and R2 is a resistor R
2, I1 is the current flowing through the transistor Q1, and Vbe is the voltage drop between the base and the emitter of the transistor Q2. When the photocurrent Ipd flowing through the transistor Q1 changes from the “H” level to the “L” level, the electric charge accumulated at the base of the transistor Q3 becomes
It is pulled out by the transistor Q1.

As described above, according to the optical receiver using the current-voltage converter according to the first embodiment of the present invention, the photocurrent Ipd of the transistor Q1 is changed from “H” level to “L” level. When the change occurs, the charge accumulated in the base of the transistor Q3 is extracted by the transistor Q1, so that the output waveform sharply changes as shown in FIG. 3A as compared with the conventional case using a clamp diode. Can be shut down.

Accordingly, the dynamic range of the optical receiver can be widened by causing the output waveform to fall sharply as compared with the conventional example. An analog-digital converter or the like connected at the subsequent stage can accurately convert the pulse width of the input signal into binary data. Further, according to the current-to-voltage converter according to the present invention, since the current flowing through the transistor Q1 is determined by the constant current source I1, the collector current of the transistor Q1 can be kept constant even if the power supply voltage changes. As a result, the transistor Q
Since the frequency response characteristic of No. 1 is stabilized, the frequency output characteristic of the optical receiver is also stabilized.

Further, according to the current-to-voltage converter of the present invention, considering the operation limit of the circuit at the time of low voltage driving, the circuit is operated until the power supply voltage VCC becomes equal to or less than the resistance drop (R1 + R2) + 2 × Vbe. Can be operated. In addition,
Vbe is a voltage drop between the base and the emitter of the transistor Q1 and the transistor Q2. Therefore, low voltage driving of the optical receiver can be achieved.

As a result, the voltage range of the driving power supply is wide,
Moreover, an optical receiver having a wide dynamic range can be provided. In the current-voltage converter according to the present invention, the DC feedback circuit 13 that has detected the voltage across the resistor R3 converts the voltage across the resistor R3 into a transistor Q1.
The base potential is adjusted by feeding back to the base, and this can be removed when a DC offset (signal component due to extraneous light) is superimposed on the input signal.

In the DC feedback circuit 13A,
By providing a low-pass filter as shown in FIG. 2B, the high-frequency cutoff frequency fL of the current-to-voltage converter can be determined as shown in FIG. 3B. Further, in the embodiment of the present invention, as shown in FIG. 4, a field effect transistor TN is provided as a clamp transistor instead of the transistor Q3. Transistor T
The gate of N is connected to the collector of transistor Q1, the source is connected to the base of transistor Q1, and the drain is connected to power supply line VCC. Then, the transistor TN adjusts the threshold value Vth to a value larger than the voltage drop Vbe between the base and the emitter when the transistor Q2 is turned on.

In this way, the transistor TN can be turned on when the photocurrent Ipd is at "H" level which is much larger than the normal amplitude. Thus, the resistor R1 for determining the operating voltage of the transistor TN can be omitted, which contributes to circuit integration. (2) Second Embodiment FIG. 5 shows a configuration diagram of an optical receiver using a current-voltage converter according to a second embodiment of the present invention. The second embodiment differs from the first embodiment in that the current-voltage converter 22 is provided with a Schottky barrier diode. In FIG. 5, reference numeral 22 denotes a current-voltage converter for converting the photocurrent Ipd flowing through the light receiving element 11 into a voltage.
The SBD is a Schottky barrier diode that prevents the voltage at the collector of the transistor Q1 from lowering with reference to the base potential of the transistor Q1. The cathode of the SBD is connected to the collector of the transistor Q1, and the anode is connected to the base of the transistor Q1. Note that components having the same reference numerals and names as those in the first embodiment have the same functions, and a description thereof will be omitted.

Thus, according to the optical receiver using the current-voltage converter according to the second embodiment of the present invention, the Schottky barrier diode is connected between the base and the collector of the transistor Q1. So the transistor Q
With reference to the base potential of 1, the voltage of the collector can be prevented from dropping. As a result, even if the amplitude of the base input is large, the circuit operation is stabilized because the collector voltage of the transistor Q1 does not decrease.

(3) Third Embodiment FIG. 6 shows a configuration diagram of an optical receiver using a current-voltage converter according to a third embodiment of the present invention. The third embodiment differs from the first embodiment in that a constant voltage diode is provided in the current-voltage converter 32. In FIG. 6, reference numeral 32 denotes a current-voltage converter for converting the photocurrent Ipd flowing through the light receiving element 11 into a voltage. D11 is a diode for preventing the voltage of the collector of the transistor Q1 from falling with reference to the power supply line VCC. The cathode of D11 is connected to the collector of transistor Q1, and its anode is connected to power supply line VCC. Note that components having the same reference numerals and names as those in the first embodiment have the same functions, and a description thereof will be omitted.

As described above, according to the optical receiver using the current-voltage converter according to the third embodiment of the present invention, the diode D11 is connected to the collector of the transistor Q1 and the power supply line V.
Since the power supply line is connected between the power supply line Vcc and the power supply line Vcc, the voltage of the collector can be prevented from lowering. As a result, even when the amplitude of the base input is large, the circuit operation is stabilized because the collector voltage of the transistor Q1 does not decrease as in the second embodiment.

(4) Fourth Embodiment FIG. 7 shows a configuration diagram of an optical receiver using a current-voltage converter according to a fourth embodiment of the present invention. The fourth embodiment differs from the first embodiment in that the transistor of the current-voltage converter 42 is an n-type field effect transistor.

In FIG. 7, reference numeral 42 denotes a current-voltage converter for converting the photocurrent Ipd flowing through the light receiving element 11 into a voltage. The conversion circuit 42 includes three n-type field effect transistors (hereinafter simply referred to as transistors) TN1 to TN3, three resistors R1 to R3, two constant current sources I1 and I2, and 1
It consists of two capacitances C1. The transistor TN1 is an example of a first field-effect transistor, and its gate (input) is connected to the light receiving element 11, the source of the transistor TN3, and one end of the resistor R3, and its drain is connected to the gate of the transistor TN3 and one end of the resistor R1. Connect to each. The source of the transistor TN1 is connected to the constant current source I1 and one end of the capacitance C1. The other end of the constant current source I1 and the other end of the capacitance C1 are connected to a ground line GND. The other end of the resistor R1 is connected to the gate of the transistor TN2 and one end of the resistor R2. The other end of the resistor R2 is connected to the power supply line VCC. The value of the resistor R2 is desirably set so that the transistor TN3 is cut off when there is no input to the transistor TN1.

The transistor TN2 is an example of a second field-effect transistor. The drain of the transistor TN2 is connected to the power supply line VCC, and the source is the output, the other end of the resistor R3, and the constant current source I.
2 respectively. The other end of the constant current source I2 is connected to the ground line GND. The transistor TN3 is an example of a third field-effect transistor, and forms a clamp transistor as in the first to third embodiments. Its drain is connected to the power supply line VCC. The transistor TN3 clamps the transistor TN1. The transistor TN3 turns on when the photocurrent Ipd flowing through the light receiving element 11 increases. At this time, the ON condition of TN3 is T
This is when the gate potential of N1 decreases, the drain current of TN1 decreases, and the drain voltage increases. When the transistor TN3 is turned on, a current flows from the power supply line VCC to the light receiving element 11, and the gate potential of the transistor TN1 is fixed to prevent the drain potential from lowering. Note that components having the same reference numerals and names as those in the first embodiment have the same functions, and a description thereof will be omitted.

Next, the operation of the optical receiver using the current-voltage converter according to the fourth embodiment of the present invention will be described. For example, when the photocurrent Ipd does not flow through the transistor TN1,
The DC potential of the input V1 and the output V2 of the current-voltage conversion circuit 42 are the same. The DC potential of the input V1 and the output V2 is substantially equal to the voltage drop R2 ·
The potential becomes (い た VCC-R2２I1-Vth) obtained by subtracting I1 and the threshold value Vth of the transistor TN2.

The source potential of the transistor TN1 is equal to the current minus
It becomes a DC voltage (V1−Vth) obtained by subtracting the threshold value of the transistor TN1 from the input V1 of the voltage conversion circuit 42. Further, since the source of the transistor TN1 is grounded in an AC circuit by the capacitor C1, this transistor circuit is a so-called grounded source circuit. Further, since the input V1 and the output V2 of the current-voltage conversion circuit 42 have the same potential, D
The C feedback circuit 13 does not feed back the control signal to the input V1 of the transistor TN1. On the other hand, the threshold value Vth of the clamping transistor TN3 is different from that of the other transistors TN1 and TN3.
Since it is larger than the threshold value Vth of N2, the other transistors TN
Unless a gate voltage higher than the gate voltage of TN2 is input, the transistor TN3 does not turn on. Therefore, the drain current I1 does not flow through the transistor TN3 at this time.

Next, when the photocurrent Ipd flows through the transistor TN1, the output V2 of the current-voltage conversion circuit 42 becomes ΔV
V2 = ΔIdd × R3. Here, ΔV2 is a change in the output of the current-voltage conversion circuit 42, and ΔIpd is a change in the photocurrent Ipd flowing through the transistor TN1. R3 is the value of the resistor R3. Thus, the current-voltage conversion circuit using R3 as the transimpedance operates.

If the current when the photocurrent Ipd is at the “L” level is IpdL and the current when the photocurrent Ipd is at the “H” level is IpdH, the change in the input current is ΔIpd =
Since IpdH-IddL, the output V2 of the current-voltage conversion circuit 42 is ΔV2 = ΔIdd × R3. On the other hand, when the amplitude of the photocurrent Ipd flowing through the transistor TN1 is large, the drain current of the transistor TN1 decreases and the drain potential increases. Thus, the transistor TN3 is turned on by increasing the gate voltage of the transistor TN3, so that current is drawn from the power supply potential and the transistor TN1 is clamped. The current-voltage conversion circuit 4 at this time
2, the relationship of ΔV2 = ΔIpd × R3 described above does not hold, and the output V2 becomes V2 = VCC−
R2 · I1-Vth.

Here, V2 is D of the current-voltage conversion circuit 42.
C is a power supply voltage, VCC is a power supply voltage, and R2 is a resistor R
2, I1 is the current flowing through the transistor TN1, and Vth is the threshold value of the transistor TN2. When the photocurrent Ipd flowing through the transistor TN1 changes from the "H" level to the "L" level, the charge stored in the gate of the transistor TN3 is extracted by the drain of the transistor TN1.

As described above, according to the optical receiver using the current-voltage converter according to the fourth embodiment of the present invention, the gate input of the transistor TN1 changes from “H” level to “L” level. At this time, the electric charge accumulated in the gate of the transistor TN3 is extracted by the transistor TN1, so that the output waveform can fall sharply similarly to the first embodiment.

Therefore, similarly to the first embodiment,
The dynamic range of the current-voltage conversion circuit 42 can be widened. An analog-to-digital conversion circuit or the like connected downstream of the optical receiver can accurately convert the pulse width of the input signal into binary data. Further, according to the current-voltage converter according to the present invention, the transistor T
Since the current flowing through N1 is determined by the constant current source I1, the drain current of the transistor TN1 can be kept constant even if the power supply voltage changes. As a result, the frequency response characteristics of the transistor TN1 are stabilized, so that the frequency output characteristics of the optical receiver are also stabilized.

Further, according to the current-to-voltage converter of the present invention, as in the first embodiment, when considering the operation limit at the time of low-voltage driving of the circuit, the power supply voltage VCC has a resistance drop (R1 + R2 ) The circuit can be operated until it becomes equal to or less than + 2 × Vth. Therefore, low voltage driving of the optical receiver can be achieved. Vth is a threshold voltage of the transistor TN1 or the transistor TN2.

Thus, similar to the first embodiment,
An optical receiver having a wide voltage range of a driving power supply and a wide dynamic range can be provided. Further, since the current-voltage converter 42 is composed of the n-type field effect transistors TN1 to TN3, the circuit can be integrated. In the embodiment of the present invention, by adjusting the threshold Vth of the transistor TN3 to a value larger than the threshold Vth of the transistor TN2, when the photocurrent Ipd is at the “H” level which is much larger than the normal amplitude, The transistor TN3 can be turned on. Thus, the resistor R1 that determines the operating voltage of the transistor TN3 can be omitted. Therefore, circuit integration can be achieved.

[0068]

As described above, according to the current-to-voltage converter of the present invention, when the base input of the first transistor changes, the electric charge accumulated in the base of the third transistor is reduced to the first level. Since it is extracted by the transistor, the output waveform can be sharply lowered as compared with the case of using the clamp diode as in the conventional example. For this reason, the dynamic range of the current-voltage converter can be widened.

According to another current-to-voltage converter of the present invention,
Since the Schottky barrier diode is connected between the base and the collector of the first transistor, it is possible to prevent the voltage of the collector from being lowered with reference to the base potential of the first transistor. Further, since the diode is connected between the collector of the first transistor and the first power supply line, the voltage of the collector can be increased with reference to the first power supply line. As a result, even when the amplitude of the base input is large, the circuit operation is stabilized because the collector voltage of the first transistor does not decrease.

According to the current-voltage converter of the present invention, since the signal input circuit and the signal output circuit are constituted by the field effect transistors, the circuit can be integrated. According to the optical receiver of the present invention, the current-voltage conversion circuit is the current-voltage conversion circuit of the present invention.
Since it is constituted by the voltage converter, the voltage range of the driving power supply can be widened, and the dynamic range of the current-voltage converter can be widened.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical receiver using a current-voltage converter according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a DC feedback circuit according to each embodiment of the present invention.

FIG. 3 is a diagram comparing output waveforms of the optical receiver according to each embodiment of the present invention and a conventional optical receiver, and a frequency characteristic diagram of the optical receiver.

FIG. 4 is a configuration diagram of an optical receiver using another current-voltage converter according to the first embodiment of the present invention.

FIG. 5 is a configuration diagram of an optical receiver using a current-voltage converter according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical receiver using a current-voltage converter according to a third embodiment of the present invention.

FIG. 7 is a configuration diagram of an optical receiver using a current-voltage converter according to a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram of an optical receiver using a current-voltage converter according to a conventional example.

[Explanation of symbols]

1,11 ... light receiving element, 2,12,22,32,42 ... current-voltage conversion circuit, 3,13 ... DC feedback circuit, Q1-Q3, Q11, Q12 ... npn-type bipolar transistor, Q13-Q15 ... pnp Type bipolar transistors, TN1 to TN3... N-type field effect transistors, R
1 to R3: resistor, I1, I2, I11, I12: constant current source,
C1, C11: capacitance.

────────────────────────────────────────────────── ─── of the front page continued (51) Int.Cl. ⁷ identification mark FI H04B 10/28 (56) references Tokuoyake flat 7-52371 (JP, B2) (58 ) investigated the field (Int.Cl. ⁷ H03F 3/08 H04B 10/04 H04B 10/06 H04B 10/14 H04B 10/26 H04B 10/28

Claims (10)

(57) [Claims] A first transistor having a base connected to the input; a first resistor having one end connected to a collector of the first transistor; one end connected to the other end of the first resistor; A second resistor having the other end connected to the first power supply line, a base connected to a connection point between the first resistance and the second resistance, and a collector connected to the first power supply line. A second constant current source having one end connected to the emitter and the output of the second transistor and the other end connected to the first power supply line; and one end connected to the emitter of the second transistor. And a third resistor having the other end connected to the base of the first transistor; one end connected to the emitter of the first transistor; and the other end connected to the second power supply line. A second constant current source, one end of which is connected to the first transistor. Connected to the emitter of the motor, and a capacitance connected to the other end to a second power supply line, a base connected to the collector of said first transistor,
Connecting an emitter to the base of said first transistor;
And a third transistor having a collector connected to the first power supply line. 2. A current-supply circuit according to claim 1, further comprising a feedback circuit for detecting a voltage between both ends of said third resistor and adjusting a base potential of said first transistor.
Voltage converter. 3. The current-to-voltage converter according to claim 2, wherein a low-pass filter is provided in the feedback circuit. 4. The method according to claim 1, wherein the value of the second resistor is set so that the third transistor is cut off when there is no input to the first transistor. Voltage converter. 5. In place of the third transistor, a gate is connected to a collector of the first transistor, a source is connected to a base of the first transistor, and
A field-effect transistor having a drain connected to a first power supply line is provided, wherein the field-effect transistor is adjusted to a threshold voltage larger than a base-emitter voltage at which the second transistor turns on. The current-voltage converter according to claim 1. 6. The Schottky barrier diode according to claim 1, further comprising a Schottky barrier diode having a cathode connected to the collector of said first transistor and an anode connected to the base of said first transistor. Current-voltage converter. 7. The current-voltage converter according to claim 1, further comprising a diode having a cathode connected to the collector of the first transistor and an anode connected to the first power supply line. vessel. 8. A first field-effect transistor having a gate connected to the input, a first resistor having one end connected to the drain of the first field-effect transistor, and one end connected to the other end of the first resistor. A second resistor having the other end connected to the first power supply line, a gate connected to a connection point between the first resistor and the second resistor, and a drain connected to the first power supply line. A second field effect transistor connected to the first field effect transistor, one end of which is connected to the source and output of the second field effect transistor, and the other end of which is connected to the first power supply line.
A third resistor having one end connected to the source of the second field-effect transistor and the other end connected to the gate of the first field-effect transistor, and one end connected to the first field-effect transistor. A second constant current source connected to the source of the field effect transistor and the other end connected to the second power supply line; one end connected to the source of the first field effect transistor; A capacitance connected to a second power supply line; a gate connected to the drain of the first field effect transistor; a source connected to the gate of the first field effect transistor; A current-to-voltage converter comprising a third field-effect transistor connected to a power supply line. 9. The current according to claim 8, wherein the threshold voltage of the third field-effect transistor is set to a value larger than the threshold voltages of the first and second field-effect transistors. A voltage converter. 10. A light receiving element for converting received light into a current, and a current for converting a current flowing through the photoelectric element into a voltage.
And a voltage conversion circuit, wherein the current-to-voltage conversion circuit is configured as described in claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, claim 8, or claim 9. An optical receiver comprising the current-voltage converter according to any one of the above.